Saturday, December 19, 2009

Earlier this week I was contacted by Tammy Davis, Project Leader of the Alaska Department of Fish and Game Invasive Species Program. She sent me a few photos of a mysterious frog that turned up in a Christmas Tree in Alaska. The person who had bought the tree was curious about the frog, and sent in the photos to Tammy. The photos were clearly a Pacific Chorus Frog (Pseudacris regilla, also known as the Pacific Treefrog). According to Tammy, the trees originated in Oregon. This is not the first time that Pacific Chorus Frogs and other amphibians have been found to be transported in Christmas Trees and other horticultural products; for instance, Christy et al (2007 Diversity and Distributions) report on Pacific Chorus frogs being brought to Guam in Christmas Trees.

I've been studying the Pacific Chorus Frog since 1999. Most of the time, when I am thinking about conservation biology and pacific chorus frogs, it is from the perspective of potential threats that could damage their populations. However, the observation of Pacific Chorus Frogs hitchhiking from Oregon to Alaska raises the question of whether there is real potential for them to become established in Alaska. There are already several cases of these frogs being established out of their native range. For instance, a population of Pacific Chorus Frogs that was established in the Alexander Archipelago of Alaska in the 1960s was extant at least until 2002. However, it did not appear to have spread beyond a single lake, according to S.O. MacDonald's "Amphibians and Reptiles of Alaska". This suggests that perhaps Pacific Chorus Frogs would not spread far if introduced in Alaska.

In contrast, Reimchen (1991, Canadian Field Naturalist) reported on his studies of Pacific Chorus Frogs introduced to the Queen Charlotte Islands, British Columbia. The Pacific Chorus Frogs on the Queen Charlotte Islands spread at a rate of approximately 2 km per year. While the Queen Charlotte Islands are considerably south of Juneau, the islands are also north of the natural geographic range of these frogs. This suggests that Pacific Chorus Frog populations introduced to Alaska may be capable of increasing in size and spreading.

The observation of these frogs being moved so far in Christmas Trees has also made me think about the consequences of frogs being moved around within their natural geographic range. It is well-known that amphibians are transported with horticultural and agricultural products. However, it is not known whether these movements have much of an effect on local populations. Do these movements alter the population-genetic structure of any of these species? Are these movements associated with the introduction or spread of pathogens like Chytrid Fungus or Ranavirus? These are all questions worth answering.

Pacific Chorus Frogs in Christmas Trees in Alaska turned into a news story, and I have had a few people point it out to me. The comments section of these stories are predictable. They range from people upset about the recommendation to kill the frogs, to other people complaining about endangered species, but in skimming the comments, I don't see anyone else reporting finding a frog. With this increased publicity, it will be interesting to see if there are more reports of pacific chorus frogs turning up in imported Christmas Trees in Alaska.

I have also seen a rise in hits on my Pacific Chorus Frog webpage, that corresponds to the release of this story. I wonder if all this extra web traffic is from people concerned about the invasive potential of pacific chorus frogs? If you've found a Pacific Chorus frog or other amphibian in your Christmas tree, I'd be interested in hearing about it. Please send me an email at 'mfbenard@gmail.com'.